Tires for conventional sized automobiles are mounted on wheel rims that are of essentially one piece construction. The beads at the inner perimeter of the rubber tire are flexible and stretchable to the extent that they can be slightly deformed so as to pass over the side flanges of the wheel rim and become seated on the rim between the side flanges.
When the size of the rubber tire is increased, the strength of the beads is also increased, usually with the placement of more or stronger cords that extend annularly within the beads of the tire. Because of this increased strength capacity, it is much more difficult to stretch and/or deform the beads of large and stronger tires in order to place the beads on a unitary rim structure.
To permit ease of mounting and demounting tires on wheel rim structures, a five piece rim structure was developed which could be assembled as the tire is being mounted on the rim structure. Typically, the five piece rim structure includes a cylindrical rim base which can be formed of an annular center section and opposed annular back section and gutter section, all welded together into a unitary cylindrical structure. A separately formed annular inner side flange is mounted on the rim base and held in place on the back section of the rim base by a protruding flange of the rim base. A substantially cylindrical bead seat is telescopically mounted on the gutter section of the rim base, and an annular outer side flange mounts on the bead seat and is held in place by a protrusion of the bead seat. The bead seat, in turn, is held in place by a lock ring that engages in a lock ring groove of the rim base. Typically, the rim base is placed on a support surface, such as the floor of a building, with its axis of rotation oriented vertically, and the inner side flange is telescopically mounted about the rim base and held in place adjacent the floor by the additional thickness of the back section of the rim base. Next, the annular beads of the rubber tire are telescopically moved about the rim base, to place the rubber tire on the rim structure. Lastly, the outer side flange is telescopically fitted about the bead seat, and the bead seat telescopically fitted about the gutter section of the rim base, and the lock ring snapped in place behind the bead seat. With the tire assembled in this manner, the tire is inflated and ready for mounting to a vehicle.
One of the major problems with the above noted five piece wheel rim is that during use of the rim and its tire on a large vehicle, there are many instances where the vehicle rapidly accelerates or decelerates and the tire, having traction with the ground, resists spinning with respect to the ground while the wheel rim is responding to the drive train of the vehicle in an attempt to force the tire to rotate. This results in relative movement of the rubber tire with respect to the steel wheel rim. More particularly, the frictional engagement between the inner side flange and the rubber tire is sufficient to cause the inner side flange to move in unison with the tire while the rim base moves either faster or slower than the tire. This causes relative movement between the inner side flange and the rim base, and the result is fretting or deterioration of the material of the facing surfaces of the inner side flange and the rim base. Over time, the fretting becomes so serious as to cause failure of the inner side flange and/or the rim base. The deterioration can cause air leakage between the parts, partial or complete separation of the parts, and injury to the equipment and to the personnel operating or adjacent the equipment.
The typical five piece wheel rim structures which are used for very large vehicles, such as earth movers and large dump trucks weighing 100 tons or more, have a cold tire pressure of over 100 lbs. psi. This tire pressure could easily rise to 140 lbs. psi as the air, tires and wheels heat during use of the vehicle. This tends to build up an enormous potential energy within the tires this size, and there is a hazard that the side flanges of the five piece rim structures could release under the force of the compressed air in the tire, creating extreme risk to people and equipment adjacent the wheel. The release of the side flange could be caused by cracks in the flange or by fretting of the flange which occurs at the facing surfaces of the side flange and the rim base.
Also, the prior art five piece rim structures require replacement because of the hazard of a failure of the side flanges, and possibly other components, of the rim structure. One of the causes of frequent replacement of the components of the typical five piece rim structure is that the components were rolled without forging and butt-welded by an electric weld system, and cold formed in a closed die. U.S. Pat. No. 5,335,706 to Foster discloses the process of producing a forged annular flange for a five piece wheel assembly for supporting the side wall of a tire. While the forging of the annular flange is likely to increase the strength and resistance of fretting of the facing surface of the flange, the strength of the overall structure is not similarly increased. For example, the holding flanges of the bead seat and of the back section of the rim base are not increased in strength.
Fretting of the parts of the wheel rim is not exclusively experienced between only the inner side flange and the rim base. Typically, fretting to a lesser extent is also experienced between the outer side flange and the bead seat, mainly due to the same circumstances, where the outer side flange tends to rotate with the tire and the bead seat tends to rotate with the rim base. However, because of the three piece construction of the outer side flange, bead seat and gutter section, and the relative movement possible between the rim base and the bead seat, the effect of the relative movement is less pronounced at this site of the wheel rim.
As the size of the vehicles and wheels increases due to the demand for more efficient and larger scale work projects, the problem of wheel fretting becomes more pronounced.
Three piece wheel rims which reduce the number of pieces of the wheel rim are available for intermediate sized tires. The typical three piece wheel rim includes a combination rim base and inner side flange, and a combination bead seat and outer side flange and a lock ring which holds the bead seat and outer side flange on the rim base. Typically, the prior art three piece wheel rims are formed products, in that they are made from rectilinear preformed mill sections which are acquired from steel vendors. The rectilinear pre-formed sections are cut to the proper length, and then the sections are formed by rolling and forming machines into cylindrical shapes. This is known as "hooping up the sections." The adjacent ends of the hooped up sections are butt-welded together to form continuous cylindrical rims, and the excess of the butt-weld is removed by a scarfing machine.
The hooped up welded sections are fed to machines which alternately expand and compress the sections to their dimensional requirements. The sections are then put into a vertically oriented machining center and machined to final specifications.
Once the separate cylindrical sections are formed, the sections are mated and tack welded together. This completes the rim base and inner side flange as one piece and the bead seat and outer side flange as another piece. After the tack welding has been completed, the assembled sections are put into a welding machine that forms circumferential welds at the abutting edges of the sections. After the rims are made, the rim welds are tested and cleaned with a grinder and painted. The three pieces, including the lock ring, are assembled and the completed rim is ready for shipment to the customer.
While the three piece wheel rim has been successfully used for tires of average sized industrial vehicles, the rims are not strong enough for reliable and durable use by the very large vehicles that are currently being used and being developed for future use. The prior described forming process does not provide the desired strength at the intersection of the side flanges with the cylindrical rim base or with the cylindrical bead seat, causing a likelihood of failure at the positions of maximum stress at the intersections of the side flanges and their cylindrical components.